1. Field of the Invention
The present invention is related to key pads, and more particularly to key matrices that are scanned for decoding which key, if any, is depressed.
2. Background Information
Most keypad and key board interfaces, especially in cell phones and other mobile devices, are implemented with parallel wires that carry scan and sense signals. For example, 12 keys might be arranged with three scan lines and four sense lines to be able to decode which key is being depressed. Similarly, twenty keys might require four scan lines and five sense lines. Of course, other combinations of scan and sense lines may be used.
The point is that the typical micro-processor in cell phones requires a parallel connection to a keypad that traverses the hinge flex cable. The parallel connections carry the scan lines that are driven by the micro-processor and the parallel sense lines that return from the keypad. As the number of keys increases and devices become smaller, it would be advantageous to reduce the number of wires sent across the hinge flex cable of a flip or slider cell phone. The present invention provides a more efficient, more reliable use of wires in a flex cable (sometimes called flex circuit). More wires in the flex cable suggest a larger cable or smaller wires of a combination of both. Either approach reduces reliability.
The present invention provides for a reduced number of wires that traverse the hinge compared to the parallel wires of the prior art.